1. Field of the Invention
The present invention relates to sealing means between an annular combustion chamber and a turbine nozzle in a turbomachine such as an airplane turboprop or turbojet.
A turbomachine combustion chamber comprises two coaxial walls forming surfaces of revolution constituting respectively an inner wall and an outer wall that define the combustion chamber between them, each of which walls is connected at its downstream end to a respective annular flange for fastening to a casing of the turbomachine.
A sectorized turbine nozzle is arranged at the outlet from the chamber and comprises one or more annular platforms (for example two platforms comprising respectively an inner platform and an outer platform), which platforms are connected together by substantially radial vanes. The inner and outer platforms of the nozzle extend substantially axially in line with the inner and outer walls respectively of the chamber. The upstream ends of the nozzle platforms are axially separated from the downstream ends of the chamber walls by annular spaces so that the chamber walls and the nozzle platforms are capable of expanding freely while the turbomachine is in operation.
Sealing means are interposed axially between the downstream ends of the chamber walls and the upstream ends of the platforms of the nozzle in order to limit the outward passage of hot gas from the inside of the chamber towards the outside of the chamber via the above-mentioned annular spaces between the chamber and the nozzle.
First sealing means are mounted between the downstream end of the outer wall of the chamber (or between the fastener flange of said wall) and the upstream end of the outer platform of the nozzle in order to limit the radially-outward passage of hot gas between the chamber and the nozzle. Second sealing means are mounted between the downstream end of the inner wall of the chamber (or between the fastener flange of said wall) and the upstream end of the inner platform of the nozzle in order to limit the inward radial passage of hot gas between the chamber and the nozzle.
2. Description of the Related Art
In the prior art, each of the sealing means is formed by strips of circumferential orientation that are placed circumferentially beside one another around the axis of the chamber, each strip being fastened to the upstream end of the platform of a nozzle sector, and bearing against the downstream end of the chamber wall or against its fastener flange. Each of the sealing means further includes gasket covers that are mounted between the adjacent strips in order to close the spaces between the strip, and thus limit the passage of hot gas through those spaces.
The number of strips is equal to the number of nozzle sectors, and each strip is fastened on a nozzle sector by two rivets and is associated with a spring that urges it axially towards the chamber. When the turbine nozzle is made up of eighteen sectors, each of the sealing means comprises eighteen strips, eighteen gasket covers, eighteen springs, and thirty-six rivets, which constitutes a large number of parts. Those sealing means are therefore relatively complex and the time required for mounting them is relatively lengthy. Furthermore, those sealing means are not very reliable.
Because of differential thermal expansions between the chamber and the nozzle sectors, and because of the vibration to which the various parts of the sealing means are subjected in operation, it is found that the strips do not always bear against the chamber, in particular during transient operating conditions of the turbomachine. In operation, the nozzle sectors may become slightly offset in the axial direction relative to one another, thereby causing the strips to be separated from the chamber and thus preventing said strips from bearing against the chamber. In the prior art, the strips are caused to bear against the chamber along a circular line, which line can thus become interrupted as a result of the above-described phenomena. It has also been observed that the gasket covers then do not provide good sealing between the strips and that hot gas can pass between the strips to the outside of the chamber. The downstream end of the chamber wall and the fastener flange of said wall are then exposed locally to high temperatures, thereby giving rise to stresses and increasing the risk of cracking appearing in said elements.